Lippert has been hospitalised at Seoul's Severance Hospital since Thursday when a knife-wielding man slashed him on the face and left arm during a breakfast forum in Seoul.

Media images showing the bleeding ambassador shocked many in South Korea, a US ally, and caused an outpouring of public sympathy. President Park Geun-hye visited Lippert while activists held a series of pro-US rallies near the US Embassy in Seoul.

Doctors have removed the 80 stitches needed to close the cut on Lippert's face, Severance's general director Yoon Do-heum told reporters. He said the ambassador still feels some pain in his arm, but it is manageable with medicine. He may experience sensory problems in his left hand for severalmonths.

The alleged attacker, known as an anti-US activist who was previously convicted of hurling a piece of concrete at the Japanese ambassador in Seoul in 2010, was arrested on Friday. Kim Ki-jong could face charges including attempted murder.

Police said the motive for Kim's action was not known, but he shouted after the attack that he opposes the ongoing annual US-South Korea military drills that North Korea condemns as a preparation for a northward invasion.

Critics have raised fears that Park's conservative government might use the attack to crack down on those seen as pro-North Korea. Already they say Park's government infringes on freedom of speech in the name of coping with North Korea sympathizers.

Last year, a Korean-American woman accused of praising North Korea was deported, and the Constitutional Court ordered the dissolution of a small leftist party that officials say advocated a North Korean-style socialist system.

The two Koreas are divided along the world's most heavily fortified border, and the Korean Peninsula is still technically at war since the 1950-53 Korean War ended with an armistice, not a peace treaty. The US, which fought alongside South Korea during the war, stations about 28,500 troops in the South as a deterrent against the North.